Classification by Texture
- Aphanitic Texture: Fine-grained, rapid cooling
(e.g., Basalt, Andesite).
- Phaneritic Texture: Coarse-grained, slow cooling
(e.g., Granite, Gabbro).
- Porphyritic texture: A phenocryst (large crystal)
enclosed in a “groundmass” of smaller crystals.
Classification by Silica Content or (Proportion of Dark
Minerals)
- Ultramafic Rocks: Very low silica, high in iron and
magnesium (e.g., Peridotite).
- Mafic Rocks: Low silica, rich in iron and magnesium
(e.g., Basalt, Gabbro).
- Intermediate Rocks: Moderate silica content (e.g.,
Diorite, Andesite).
- Felsic Rocks: High silica content, rich in quartz
and feldspar (e.g., Granite, Rhyolite).